Four of the UK's biggest energy companies are to be investigated to see if they have breached rules on telephone and doorstep selling.

Npower, Scottish and Southern, Scottish Power and EDF will be questioned by industry regulator, OfGem.

BBC News website readers have been sharing their experiences:

Patrick Jones, Hampton Wick

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"I raised a complaint ... that they had mis-sold me the deal"

A salesman came to our door in May last year on a Sunday afternoon.

He said I should be paying £35 a month for my electricity, which I questioned as it was half the cost of my current supplier.

But as I thought I was currently paying too much and was unhappy with my then supplier, I gave him details of my general electric usage and he said again that £35 sounded right.

My first quarterly bill came and it was an estimate, bizarrely their estimate was around £50 a month - not the £35 the salesman had said.

When I gave them an actual reading it was a little over £50 and I had to pay the remainder as a one-off bill. They then changed me to a £50 direct debit to cover the costs.

I have been paying £50 a month for the past six months and just got my annual review which said I owed them nearly £500 as my direct debits were not covering my actual usage.

I raised a complaint with the company that they had mis-sold me the deal, and that my bills now are even higher than they were previously. I asked for my meter to be checked which I am doing now.

Darron Blair, Coventry

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"I felt like I was constantly being beaten with a big stick"

I was recently employed by one of the major energy suppliers and will confirm that all is not what it seems in the world of energy sales. I have a background in financial services but have never come across such bullish and high-pressure tactics from a manager.

My first eight days were spent in the office on a training course, which involved sitting exams you cannot fail. Then you join your team and away you go. This is where the problem starts. From day one your manager tells you in no uncertain terms this is about sales and signing business regardless how you get it.

During the next few days you go out with a colleague to show you the ropes, not the way you were shown in the classroom but the real way. The easiest way to get a sale is to concentrate on the pre-payment customer, as a rule we are not supposed to sign this type of customer, the main reason being there is no way of showing a savings comparison. Therefore we cannot give them an accurate figure.

We told new customers to ignore a letter they would receive informing them that they were paying more than expected, claiming it was a standard letter.

We were put under extreme pressure from the manager, constantly receiving calls and texts asking where we were and how many sales we were on. I felt like I was constantly being beaten with a big stick.

They put you in a position where you are tempted to do unethical things - I had to leave after two months.

What the company believes is happening and what is actually happening are two different things. Too many people are being ripped off.

Ron Manuel, Dursley, Gloucestershire

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Ron Manuel was mislead by an energy firm

I changed to one of the four named companies about 12 months ago, under the promise of a cheaper tariff - I was paying £70 a month for dual fuel.

But within a month, I was told they would be increasing my direct debit payments from the agreed £60 per month to £97 per month.

I asked them why they were doing that and told them to forget it. But when I threatened to leave, I was told that I would face an early termination charge of £50.

I decided to pay the fee and left and went to another company. I'm currently paying £54 per month. I'm with another company now and not had any problems.

Misled - certainly. I am pleased they are being investigated.

Joanne Casper, Skipton, North Yorkshire

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"Everyone was a winner except me"

I was persuaded to switch - even though I was wary of doing so - after a doorstep salesman came to my house.

He said my monthly instalments would be £100 for both gas and electric based on my previous supplier's bill.

After eight months I was £450 in arrears. I switched provider and owed them £300, which I argued I should not have to pay.

I cancelled my direct debit but I didn't realise that utility companies have the right to reinstate them. They took £300 from my account leaving me in dire straights and with £40 worth of bank charges.

I called the bank in tears. I'm on my own and this is a really worrying thing to cope with. It seemed everyone was a winner except me.

I have reported them to Ofgem and am still waiting for a response.

Paul Wright, Stourbridge

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Paul Wright received bailiff letters demanding payment

In July 2009, I was paying £127 per month when one of these companies came knocking on my door.

I showed him my existing bill and he said I would pay only £70 per month with them, so I signed up for three months.

Then I received a letter saying my direct debit was going up to £129 per month.

I called them to say I thought I'd been mis-sold a product but they then sent bailiff letters demanding payment.

So in the end I switched companies and cancelled the direct debit I had with the company. I ended up paying over £500 to clear my bills.

Other comments

I changed suppliers through an agent calling at my door who promised a lower tariff as well as £200 for switching -£100 immediately and after one year the other £100. This has not materialised and on querying this, the company has not given me a satisfactory answer and I am still not sure whether I am better off with them as I cannot understand their bill. D Ludick, Kingston, Surrey

I have recently been informed that if I want to cap the costs for 2010/2011 it will cost me £46 for the year. This is an increase to the daily charges. Is this a fair figure? They have stated that if costs go down so will mine and if they go up I will not have to pay. I have taken this offer over the past few years and have probably been charged for it but this is the first time I have really paid attention to the increase. Ann Gibson, Greenock, Inverclyde

My husband and I were told by a saleswoman that we would get a better rate if we got our gas and electricity from them because my husband was disabled. Our original supplier apparently didn't send them a code and because of that we had to pay twice for the same amount of electricity. And the new company charge us twice because we have our heating on Economy 7. Given the choice I would definitely change. Both my husband and I think that we were mis-sold our energy and that it seems to cost more with them than it did before. Elizabeth Akerman, Bridgwater, Somerset

A salesman arrived at my door. He told me that my direct debit £55 wasn't covering my usage with my existing company (which was true) and if I moved to the company he represented, I could pay £65 per month and my usage would be covered. I agreed to this, but within two months my bills were put up to £75 per month and have now been at £114 per month over the last three months, even though I am currently £250 in credit. I feel as though they have stolen from me I am so angry I decided to switch my supplier again. Charlene Fallan, Dalkeith, Edinburgh

I received a call from a salesman in November 2009. I was assured he could save me money. Since then, my gas bill has gone up by 40 per cent. I am currently querying their charges and am intending to change supplier. Ivor Phillips, Poole, Dorset

As somebody who used to work for a door-to-door sales team, I can confim that we were trained to lie and mis-sell. The act was disgusting. We would pretend we were from some mythological energy board advising people on how to save money on their bills. Ultimately the aim was to trick people into thinking that they were getting a better deal and to get them to sign a document allowing them to change over. Morally I could not face working there and left after two days. The whole act was ridiculous. Andy, Leicestershire

I switched companies in 2008 and was grossly miss-quoted at £90 a month for our gas and electric. I thought this was a deal worth taking as we were paying £120 a month. So I switched and agreed to be cautious and pay £100 a month. Within six months our bills had gone up to £140 a month and three months later a stagering £185 a month. I accept that things are estimated but to be that far out was clearly a ruse to dupe us into transferrring supplier. Thomas Smith, London